I would say a 16 in all likelihood to big. I can't say for sure based on where you live. I can only speak for where I fish. I typically will carry a few in size 18 but the majority are size 20-24. Some guys here in Colorado fish them in 26 & 28. For me to fish them that small if would have to tie them to tippet at home or I would spend my day cussing up a storm dropping flies in the river as I unsuccessfully attempt to tie them on.

I usually fish an RS2 on the surface when I see fish feeding and breaking the surface but not quite sipping dries. I do carry some wire ribbed RS2 for getting down under the film a few inches. I also have some very small bead head RS2's.

Back to your original question 99.9% of the time I fish a size 20 either behind a BWO dry, or on its own just below the surface.

Match the size to what is on your water and smaller. I fish this off the back of a larger dry / terrestrial as a dropper when the fish are on emergers. I have fished them on the top dropper with a larva on point with no indicators or weight and did well.

Do not give up on the 16s they will work well during a BWO hatch (tied in olive) on the Arkansas or even on Grey Reef (tied in black and grey) early as Mayflies and BWOs start coming off.

Do not get me wrong I use the above mentioned sizes on our tail waters as well, the RS2 is a great all around pattern.

I love fishing them weighted below a size smaller or larger during a major hatch to cover my bases. During a hatch use a jerky upward motion during the drift to simulate the rising emerger. Amazing takes during a hatch.

I will also use the RS2 as a searching pattern as the flash will sometimes create a positive response for no reason at all.

This is one I am playing with now and it may be tied on a light wire scud hook with a pearl or mercury glass bead and some 0.10 lead or lead sub. wraps under the thorax. I tie them in #14 - #22... fished deep or in the surface film and they ALL work...